I like Glock pistols. I don't love them, and I'm certainly no fanboy (except for old S&W revolvers). I carried a Glock 22 on duty for the brief time I spent on a small town police department. I owned a Glock 17 that was reliable as an anvil, and killed a huge number of barnyard varmints. I respect the hell out of the Glock design, and as much as I like my M&P9C, if I were to buy another plastic pistol it would be a Glock.
The M&P has some improvements over the Glock. The components are arguably of higher quality, I like the grip angle better, and I think metal magazines fall free of the mag well better than plastic ones. I also like the fully supported chamber and conventional rifling of the M&P. But the Glock still has a couple of important trump cards. First, EVERYONE makes support items for the Glock. Want a left-handed mag pouch fitted for a Glock 19? Someone makes one. Want a slide plate with a "trucker girl" silhouette on it? Someone makes one. Second, the Glock has been around long enough to have accumulated a service history--and it's pretty good. One day, the M&P will catch up. But it will take the same 30 years the Glock has had. And it's worth noting that 30 years really isn't that long in gun tech terms. Police ALL carried revolvers from the dawn of time until the very late 1970s. Then in 1985, they all ditched their S&W 3909s, Beretta 92FS, and 1911s for the plastic "Wundernine" from Austria. And though old grumps (like me) grumbled about their "tactical tupperware", the Glock just plain worked.
And that's why I've decided that if I add another pistol to my safe, it won't be my friend's GI 1911. It will be a Gen 3 Glock 19. Additionally, I can rationalize a Glock 19 in three ways. First, I can compete with it on the cheap. Second, it is large enough to make an acceptable nightstand gun. Third, I can carry it concealed in fall and winter. Now all I have to do it sell my wife on those points and perhaps I can pick up a Glock next time I hit Sportsman's. And I'll still never be able to afford another AR15.